Mobile ad hoc networking technology (MANET) describes a self-organized, self-healing wireless interconnection of communications devices to form an independent communications network, or a network extension of a wired networking infrastructure. The most important characteristic that distinguishes MANET is the absence of a fixed infrastructure. The MANET network lacks any central server to support standard networking functions such as routing, security, neighbor discovery and data forwarding.
MANET has application to military communications networks. Security is of paramount concern in military applications. Low probability of detection (LPD), low probability of interception (LPI), low probability of enemy exploitation (LPE) and anti-jamming capability (AJ), are features that are advantageous in a mobile network for military operations. These features would also be required for other mobile network communications involving communication of confidential or classified information.
Normally, when a node attempts to join a mobile network during a neighbor discovery (ND) process, an announcement packet (AP) or message is broadcast from the node using an omni-directional antenna. The announcement packet includes the location of the node and other information necessary for the node to gain access the network. Announcement packets that are broadcast using an omni-directional transmission source are susceptible to detection or interception by enemy receivers or other unintended recipients. Since the omni-directional broadcast may be received by anyone within range, the signals should be low power to avoid detection by an enemy. This is problematic since they must be high enough in power to discover neighbors at the maximum network formation range. Furthermore, omni-directional receivers for receiving the AP signals may be easily jammed by enemy transmitters.
Typically during the ND process, the announcement messages or packets are transmitted in a different frequency from that of the network communication band in order to avoid interference with the ongoing communications between nodes already connected to the network. This additional frequency band, or out-of-band, signal consumes more of the limited RF spectrum.
In contrast to the omni-directional antenna, directional antennas, such as Phased Array Antennas (PAA) can focus radiation energy in a narrow angle to form wireless links between nodes in a network. Directional antennas have advantageous properties for communications networking such as high data transmission rates, long range communication, LPD, LPE, LPI and AJ as mentioned above. PAAs may also be electronically guided to rapidly multiplex the available bandwidth amongst multiple communicating peers. PAAs can be redirected in a few microseconds, which is a characteristic that cannot be achieved with mechanically-steered antennas.
Heretofore, directional antennas have been unsuitable for MANET, because directional antenna communications require the transmitting and receiving nodes to be aligned. Even if two nodes are within range, they cannot discover each other if their respective antennas are not aligned. Alignment of the antennas is unlikely to occur until the relative locations of both nodes are discovered by each of the nodes. The node locations have to be established by omni-directional antenna communications as described above. In that case, an additional antenna must be provided at the node, dedicated solely to the ND process, and adding additional cost and weight to the node.
Therefore, there exists a need for a mobile communications networking system and method using directional antennas for neighbor discovery and data communications.